In a conventional wireless digital transmission system, there is often a need to detect or estimate time and frequency offsets in a received signal relative to a transmitted signal. In a single frequency network (SFN), for example, detected time and frequency offsets are used to synchronize time and frequency of transmitted and received signals. As is well-known, a SFN is a broadcast network in which several transmitters simultaneously transmit the same signal over the same frequency channel. One type of conventional SFN is known as a hybrid satellite and terrestrial SFN. An example hybrid SFN is defined in the Digital Video Broadcasting-Satellite services to Handhelds (DVB-SH) standard “Framing Structure, Channel Coding and Modulation for Satellite Services to Handheld devices (SH) below 3 GHz,” DVB Document A111 Rev. 1, July 2007.
A DVB-SH SFN is a hybrid satellite and terrestrial SFN in which signals are simultaneously transmitted over the same frequency channel via both satellite and terrestrial communications links.
In a conventional DVB-SH SFN, a signal from a satellite has a varying time delay and frequency offset with respect to a terrestrially repeated signal due to the relative motion of the satellite in an inclined orbit. Because of this varying time delay and frequency offset, time and frequency synchronization is necessary to ensure proper reception of signals by receivers in the DVB-SH SFN.